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PGI-1 Talk: Prof. Dr. Alexander Grüneis

Electronic structure control of 2D matter

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30 Jan 2019 11:30
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PGI Lecture Hall

University of Cologne

Abstract:

The electronic structure of 2D matter can be controlled by chemical functionalization and the fabrication of vertical heterostructures between dissimilar 2D layers. The present talk illustrates this approach for a number of 2D materials (graphene, MoS2 and phosphorene) by employing a unique combination of ultra-high vacuum Raman/luminescence and angle-resolved photoemission spectroscopy (ARPES).
As a first example, it is shown that ionic functionalization of graphene by alkali metals enables tuning of the charge carrier density into the superconducting regime. We find a characteristic phonon frequency change with carrier concentration that is explained by the removal of the Kohn anomaly and a bond length increase upon doping. ARPES shows a “kink” feature in the pi band of graphene due to electron-phonon interaction. For ultra-large doping, we are able to shift the Fermi level beyond the van Hove singularity of graphene located in the middle of the Brillouin zone edge. The appearance of a flat band at the Fermi level is shown by ARPES and marks the Lifshitz transition in graphene.
For phosphorene, we find that chemical doping introduces a staggered potential resulting in a band inversion that is driven purely by the Coulomb interaction between individual layers [3]. Our tight-binding simulations can fully explain the observed band structure and highlight the role of glide mirror symmetry. Finally, for molecular beam epitaxy grown graphene/MoS2 heterostructures, the non-interacting nature of the two layers is shown. Surprisingly, find a narrow photoluminescence peak of MoS2 despite the metallic substrate.

Contact

Prof. Dr. Stefan Blügel
Phone: +49 2461 61-4249
Fax: +49 2461 61-2850
email: s.bluegel@fz-juelich.de

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